I like the soak-in-PB-then-warm-it-with-a-heat-g*n method. Do that, put it back in your benchtop vise With a quick release skewer holding the tool to the freewheel (not tightened all the way down, obv) and really reef on it again. I've broken free two hopeless cases that way.

I usually apply the PB for a couple of days and let it sit. And tap on the freewheel with a heavy wench or hammer to let the vibrations help it soak in. I have no idea if this actually helps, but it makes me feel I'm doing everything I can